> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lerian.studio/llms.txt
> Use this file to discover all available pages before exploring further.

# Matcher duplicate-ingestion contract

> Matcher documentation now describes configurable source duplicate keys, the FLAG_AS_EXCEPTION default, and aggregator connection testability.

<Badge stroke icon="calendar-days" iconType="regular">August 18, 2026</Badge> <Badge stroke icon="file-code" iconType="regular">Documentation correction</Badge> <Badge color="red" size="lg" stroke icon="triangle-exclamation" iconType="regular">Action required</Badge>

## Affects

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Teams that import reconciliation files, configure Matcher sources, or operate aggregator connections.

## What changed

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A source can define `duplicate_key` as an ordered list of mapped fields when `external_id` alone is not sufficient. Aggregator-bound sources cannot use a custom key. The default duplicate policy is `FLAG_AS_EXCEPTION`, not `KEEP_FIRST`, and changing a duplicate key affects later imports only.

The aggregator connection guide now also requires clients to use the list response's `testable` field before offering a connectivity test.

This is a documentation correction that aligns with the implemented contract. It does not announce a runtime release.

## Impact

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**Classification: Action required.** Existing import controls that assume silent duplicate drops can produce or handle exceptions differently from the documented default.

## What you need to do

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<Steps>
  <Step>Review each source's duplicate policy and exception handling before the next import.</Step>
  <Step>Set `duplicate_key` only when every selected field is mapped; do not configure it for aggregator-bound sources.</Step>
  <Step>Use `testable` before exposing an aggregator connectivity test in your workflow.</Step>
</Steps>

### Deadline

Complete the review before the next production reconciliation import.

## Resources

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* [Upload files to Matcher](/en/products/matcher/daily-reconciliation/matcher-uploading-files)
* [Manage aggregator connections](/en/products/matcher/integrations/matcher-aggregator-connections)